Machine for forming metal bars

ABSTRACT

A machine for forming metal bars, in particular for producing ingots made of precious metal such as gold, silver, precious alloys, as well as other pure metals or different alloys, which includes a solidification station provided with a cooling surface having passage holes and being cooled with cooling fluid. The cooling surface being made of copper, aluminium or alloys thereof or other materials suitable for the controlled dispersion of heat and having a sliding surface on which the ingot moulds are inserted and rested. The cooling fluid passes longitudinally and/or transversely to the direction of insertion of said ingot moulds.

This is a divisional application of U.S. patent application Ser. No.14/007,910, filed Oct. 17, 2013, which in turn is the National Stage ofPCT/EP2012/001377 filed on Mar. 29, 2012, which claims priority under 35U.S.C. §119 of Italian Application No. VI2011A000076 filed on Apr. 1,2011. The international application under PCT article 21(2) waspublished in English. The disclosures of the referenced applications areincorporated herein by reference.

The present invention regards a machine for forming metal bars, inparticular for producing ingots made of precious metal such as gold,silver, precious alloys, as well as other pure metals or differentalloys.

As known, producing ingots, in particular made of gold, silver, preciousalloys, other pure metals and different alloys, is usually obtained bymeans of two different methods. When producing light ingots, from 5 g upto 50 g, there is used a cold moulding and coining process, startingfrom semi-finished products, such as cylindrical-shaped preformed padsor billets.

When producing ingots with weight varying between 50 g and 50 Kg thereis instead used the melting method and subsequent solidification of themetal in the special moulds. In practice, the metal to be melted isplaced within ladles, in form of powders, granules or loose rawmaterials of various sizes, wherein it is brought to melting. Then themolten metal is poured in single ingot moulds, generally shaped to forma truncated-trapezoid wherein, solidifying, it takes the form of aningot.

Such two operations, the melting one and the subsequent one forsolidifying the material, must be carried out with special care, giventhat the obtained end-product must meet strict and specific standardrequirements.

Actually the ingots available in the market, besides having an exactpurity if made of pure metal, or an exact percentage of pure metal ifmade of an alloy (the so-called “count”), must have extremely precisedimensions and weight, an external configuration with regular surfaces,without depressions or cracks, a uniform coloration and, above all, theymust have a perfect internal metal-graphic structure, without blowholes,microporosities and structural tensions.

In order to avoid obtaining faulty ingots not capable of allowingobtaining “punching”, which would thus be considered as waste material,it is necessary that the entire production cycle be carried out withmuch care, in particular during the steps of melting, solidifying andcooling the metal.

An object of the present invention is to provide a machine for formingmetal bars, in particular for producing ingots, made of precious andnon-precious material and, which does not have the drawbacks revealed bythe plants of the known type.

The characteristics of the invention will be made more clear through thedescription of a possible embodiment thereof, provided by way ofnon-limiting example, with reference to the attached drawings, wherein:

FIG. 1 represents an elevational view of the machine according to theinvention;

FIGS. 2 and 3 represent detailed views of the ingot mould, in thesolidification station, with different cooling modes;

FIG. 4 represents three different configurations of the sliding plate ofthe ingot moulds, during the solidification step.

As observable from the drawings, the machine according to the invention,generally indicated with reference 100, comprises a station forsolidifying the molten metal, indicated with reference 104.

In the solidification station 104 the incandescent temperature ingotmoulds 1, containing the molten metal and closed by covers 4, slideuntil they stop on a cooling surface 10, cooled with water by means ofpassage holes present therewithin and made using copper, aluminium oralloys thereof or other materials suitable for the controlled dispersionof heat, in which they remain for a predefined period of time, averaging1 to 5 minutes, as a function of the amount of material to besolidified, up to the complete solidification of the entire mass.

Also in the solidification process there should be created an “inert”environment, hence there is introduced a flow of inert gas such asNitrogen, Argon or Nitrogen-Hydrogen mixture, which prevents theoxidation of the ingot moulds and the covers and protects the metalbeing solidified against oxygen.

Specifically, depending on the internal metal structure the ingot isrequired to obtain, which should have large, medium or small crystalsand a more or less marked solidification shrinkage, the solidificationstation 104 may be provided with further insulating or refractorycooling plates 11 for slowing the thermal dispersion. Such plates may bepossibly provided with notches for defining the localized heat areas,which are placed near or in contact with one or more sides of the ingotmould 1 and of the cover 4 (see FIG. 2), and/or further heating plates21 for slowing the cooling, made of graphite, metal or refractory orinsulating materials, smooth or provided with suitable millings inrelief or recessed, which may be placed between the cooling plate 10 andthe ingot mould 1 (see FIG. 3).

Alternatively, when there is required an accurate control of thethermodynamic solidification gradients, with the aim of obtaining aningot with the most suitable solidified metal structure thesolidification station 104 may be provided with heating panels 12 forexample heated using electrical resistors, gas or using any other means,also positioned around the ingot mould and on the cover.

Furthermore, with the aim of having a further possibility of accuratelydetermining the thermodynamic gradients, depending on the internal metalstructure the ingot is required to take, the cooling plate 10 may havethe sliding surface, on which the ingot moulds stop in thesolidification step, having a flat and smooth surface, or provided withmillings in relief or recessed. Furthermore, the passage of the coolingfluid may be executed longitudinally and/or transversely to thedirection of movement of the “trains” of ingot moulds (see FIG. 4).

Due to construction reasons, in some cases the solidification station isincorporated in a single station which also comprises a station ofsecondary addition wherein a chemical additive is added to the moltenmetal in ingot mold 1, which creates a chemical reaction with theimpurities in the molten metal.

The invention thus conceived can be subjected to numerous variants andmodifications and the construction details thereof can be replaced bytechnically equivalent elements, all falling within the inventiveconcept defined by the following claims.

1. A machine for forming metal bars, in particular for producing ingotsmade of precious metal such as gold, silver, precious alloys, as well asother pure metals or different alloys, utilizing ingot molds each havinga cover, said machine comprising a solidification station provided witha cooling surface, said cooling surface having passage holes and beingcooled with cooling fluid passing through said passage holes, saidcooling surface being made of copper, aluminium or alloys thereof orother materials suitable for the controlled dispersion of heat, saidcooling surface further includes a sliding surface on which the ingotmoulds are inserted and rested, said cooling fluid passing through thepassage holes of said cooling surface longitudinally and/or transverselyto the direction of insertion of said ingot moulds.
 2. The machineaccording to claim 1, wherein said cooling surface is flat and smooth.3. The machine according to claim 1, wherein said cooling surfacecomprises millings in relief or recessed.
 4. The machine according toclaim 1, wherein said solidification station comprises heating platesfor slowing down the cooling process, made of graphite, metal orrefractory or insulating materials, said heating plates being interposedbetween said cooling surface and said ingot moulds.
 5. The machineaccording to claim 4, wherein said heating plates comprise smoothsurfaces.
 6. The machine according to claim 4, wherein said heatingplates comprise surfaces provided with suitable millings in relief orrecessed.
 7. The machine according to claim 1, wherein saidsolidification station comprises cooling or thermal insulation plates,provided with notches for defining localized heat areas, said cooling orthermal insulation plates being placed near or in contact with one ormore sides of the ingot moulds and their covers.
 8. The machineaccording to claim 1, wherein said solidification station comprisesheating panels of the electrical resistor type, gas-type or heated withother means, positioned around the ingot moulds and on the covers. 9.The machine according to claim 1, wherein said solidification stationcomprises an inert environment which comprises an inert gas whichprevents oxidation of said ingot moulds and said covers and protects themetal still in liquid form against oxygen.
 10. The machine according toclaim 1, wherein said inert gas comprises nitrogen, argon ornitrogen-hydrogen mixture.
 11. The machine according to claim 1, whereinsaid solidification station is incorporated in a single station whichalso comprises a station of secondary chemical addition.